GMC Jimmy--Crankcase filled to top with gasoline! What caused this?

Hello; I'm new to the board and have already made my New Member Intro.

I have a 1993 GMC Jimmy 4x4 with the 4.3L Vortec engine and automatic transmission. It had been running rough, and getting really bad gas mileage. (for months prior to this final event) Also, it was very hard to start most of the time. It is a high mileage vehicle, around 180,000 miles. But there are no knocks in the engine, the transmission shifts great, and no major issues until now.

The first 10 digits of the VIN: 1GKDT13W1P

I check my oil and other fluid levels often. So, it was a shock when I pulled the oil dipstick and that it was showing that the oil reading was at the top of the dipstick. After a quick "smell" test, it was clear that the extra fluid is definitely gasoline. There is no doubt that itis gasoline, not coolant.

I've never pulled a plenum on one of these 4.3L engines. What is it, under the plenum, that could have broken and pump that much fuel into the crankcase? I think the Fuel Regulator is under there, and of course, other fuel injector fuel lines.

Has anyone else had this issue come up or see a story about it? My Son and I are going to drain the crankcase and start pulling the plenum tomorrow, weather permitting. Other than obvious broken lines or loose connections, what should I look for? Any help or ideas would be greatly appreciated!

The intake manifold is just a piece of cast aluminium, removing it will buy you nothing.

If you have excessive fuel being ingested, there must be a fuel leak at the throttle body. The injector(s) in the throttle body must be allowing too much fuel to be delivered; and, it is not closing when the engine is shut off, allowing fuel to be sprayed into the intake when the engine is off.

Thanks for your reply, Ray!
My son and I did go ahead and removed the upper piece of the "upper intake manifold assembly". Opening this part up revealed the Central Multiport Fuel Injector (CMFI) unit and all it's injector assembly parts. The right side (driver's side) of the lower intake manifold assembly looks "normal", like the inside of any well used engine part. But the left side was clearly the area affected by a bad leak. Everything around and directly in front of, the 1 1/4" cylindrical part, is washed clean, like a new penny, by the spraying gasoline. There's a small hole in the bottom of the lower intake manifold assembly, so this is where it was getting into the crankcase. There was also an issue on the day of the discovery, that the rear cylinder on the left side, (passenger side), was filling with gas and I would have to remove the spark plug and turn the engine over by hand to empty the cylinder of excess gas. Then, I could replace the plug and start the engine. But after I stopped and turned off the engine for any period of time, it would fill up again and the sequence would repeat.

It sounds like I may have found the part, (the CFMI unit) that needs to be replaced. I don't know how expensive they are, or how often this happens. It seems like a dangerous problem, now that I know what was actually happening inside the engine. Was there any danger of an explosion or fire with this situation?

Thanks again for any advice, similar stories, etc.

Regards, Craig (firstchoice)

According to a manual that I've found online, "Should a failure occur in any components of the CMFI unit, the entire assembly must be replaced." Does anybody have a ballpark figure of what these CMFI units cost?

Thanks for your reply, Ray!
My son and I did go ahead and removed the upper piece of the "upper intake manifold assembly". Opening this part up revealed the Central Multiport Fuel Injector (CMFI) unit and all it's injector assembly parts. The right side (driver's side) of the lower intake manifold assembly looks "normal", like the inside of any well used engine part. But the left side was clearly the area affected by a bad leak. Everything around and directly in front of, the 1 1/4" cylindrical part, is washed clean, like a new penny, by the spraying gasoline. There's a small hole in the bottom of the lower intake manifold assembly, so this is where it was getting into the crankcase. There was also an issue on the day of the discovery, that the rear cylinder on the left side, (passenger side), was filling with gas and I would have to remove the spark plug and turn the engine over by hand to empty the cylinder of excess gas. Then, I could replace the plug and start the engine. But after I stopped and turned off the engine for any period of time, it would fill up again and the sequence would repeat.

It sounds like I may have found the part, (the CFMI unit) that needs to be replaced. I don't know how expensive they are, or how often this happens. It seems like a dangerous problem, now that I know what was actually happening inside the engine. Was there any danger of an explosion or fire with this situation?

Thanks again for any advice, similar stories, etc.

Regards, Craig (firstchoice)

According to a manual that I've found online, "Should a failure occur in any components of the CMFI unit, the entire assembly must be replaced." Does anybody have a ballpark figure of what these CMFI units cost?

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learned something never new anything like that would happen, I found shopinjectors.com

Okay, I went to the Auto Parts Store this morning. The only thing left to do was buy (1) the CMFI unit, (2) a gasket set for the upper intake manifold assembly, (the Plenum), (3) an oil and oil filter change, (4) a new starter, and the vehicle would've soon been back in operation.

And then I heard the price of the CMFI unit come from the Oreilly's Auto employee.

Well, I hope my experience has helped to add to the data base of problems, parts ID'ing, and solutions for not-so-often experienced issues. I'll try to take a few pics of the repairs, parts, and the end result to post.

Thanks for your reply, Ray!
My son and I did go ahead and removed the upper piece of the "upper intake manifold assembly". Opening this part up revealed the Central Multiport Fuel Injector (CMFI) unit and all it's injector assembly parts. ?

Click to expand...

Hmmm, I thought the '93 4.3 used throttle body injection. Sorry, if I mis-lead, glad you found the problem.

Thanks for all the replies and leads on CMFI Assemblies! That's a much better price, no doubt. And thanks for the tip on the fragile fuel lines. I can't imagine getting a new one and snapping a line. The Jimmy has set since I last posted due to an injury, but I think I'll try to tackle the job with my son's help now.
I did have one thought. With the fuel in the oil like it was, should I prime the oil pump before I start the engine? It will have a new oil and oil filter change when I start it. But should I pump fresh oil up to the lifters, camshaft, bearings, etc., first? Or does the oil pump do it quick enough to avoid anymore damage than already done? This may be a redundant question.

Thanks for all the replies and leads on CMFI Assemblies! That's a much better price, no doubt. And thanks for the tip on the fragile fuel lines. I can't imagine getting a new one and snapping a line. The Jimmy has set since I last posted due to an injury, but I think I'll try to tackle the job with my son's help now.
I did have one thought. With the fuel in the oil like it was, should I prime the oil pump before I start the engine? It will have a new oil and oil filter change when I start it. But should I pump fresh oil up to the lifters, camshaft, bearings, etc., first? Or does the oil pump do it quick enough to avoid anymore damage than already done? This may be a redundant question.

Craig (firstchoice)

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Not a bad question at all. Can you get 1/2 filter full or more to begin with? If you can do that I would think it should all be ok. Engines sit for a long time and start almost dry, oil pump should be very quick.